Study of Chemical States at Intergranular Fracture Planes of Iron Alloys by Auger and Electron Energy Loss Spectroscopies

Abstract

Auger electron (AES) and electron energy loss spectroscopies (EELS) have been used tostudy the chemical states at the intergranular fracture planes (IG) of Fe-2. 7 atom % P andFe-210 atom ppm S alloys, where the concentrations of phosphorus or sulfur atoms atIG are saturated. The discussion on the chemical states was carried out by comparingthe spectra of IG with those of the transgranular fracture planes (TG), iron phosphide, iron sulfide, and the ion sputtered surfaces of the compounds. The P L_{2, 3}VV Augerspectra from TG and IG of the Fe-P alloys have five peaks, but the spectrum from Fe₃P has six peaks. The loss energies of Fe 3p EELS of TG and IG coincide with each other, andthey are different from those of Fe₃P. The apparent loss energies due to the transitionsfrom the valence to conduction bands for IG change with the kinetic energy of the primaryelectron between 200 and 500 eV. These results indicate that the phosphorus atoms areatomically dispersed in the phosphorus segregated layer at IG. The S L_{2, 3}VV Auger spectrumof the Fe-S alloy indicates that the sulfur atoms are bound to the IG planes as if theywere adsorbed. The Fe M_{2, 3}VV spectrum of TG of the alloy in Fig. 5 exhibits peaks at43. 5 (a₁) and 45. 5 (a₂) eV. The latter peak due to the Fe M_{2, 3}-Fe 3 d( 1 )-Fe 3 d( 1 )transition was observed for IG of the Fe-S alloy, but not for IG of the Fe-P alloy . Theresults indicate that at IG planes the interaction between iron and phosphorus is strongerthan that between iron and sulfur. The ion sputtering to phosphide or sulfide gives themetallic iron peaks and the spectra of phosphorus or sulfur bound to iron . This impliesthat the mixed layer of the iron and phosphorus or sulfur atoms is prepared by the ionsputtering.